effect of the waste product hydrogen peroxide. It generates radicals in the presence of acid and ketones, which accelerate the reaction by providing an additional pathway to the reactive hydroperoxide intermediate. This discovery could be applied to achieve other Brønsted acid catalyzed oxidative coupling reactions.
A direct synthesis of substituted xanthenes from salicylaldehydes and cyclohexenones or tetralones has been developed. The reaction is catalysed by Lewis acids like scandium triflate and furnishes substituted xanthenes in good to excellent yields using either microwave or thermal heating. Microwave heating results in significantly shortened reaction times of 30 min and generally higher yields.
Asymmetric Visible-Light Photoredox Cross-Dehydrogenative Coupling of Aldehydes with Xanthenes
作者:Evgeny Larionov、Marco M. Mastandrea、Miquel A. Pericàs
DOI:10.1021/acscatal.7b02659
日期:2017.10.6
cross-coupling of two C(sp3)–H bonds employing visiblelight as an economical and environmentally benign source of energy. Photoredox catalysis is used for the oxidation of a diarylmethane to the corresponding cation, which is then trapped by an enamine intermediate generated in situ from an aldehyde reactant and a secondary amine organocatalyst. Notably, this mild method is an ideal synthetic approach from the
Catalyst-free benzylic C(sp<sup>3</sup>)–H cross-coupling with organotrifluoroborates enabled by electrochemistry
作者:Chao Li、Ran Ding、Heng-Yi Guo、Shuang Xia、Lei Shu、Pei-Long Wang、Hongji Li
DOI:10.1039/d2gc02204d
日期:——
rare catalyst-free electrochemical cross-coupling of benzylic C–H bonds with organotrifluoroborates, which readily proceeds at room temperature and provides a unique protocol for forging C(sp3)–C(sp3), C(sp3)–C(sp2) and C(sp3)–C(sp) bonds. In particular, this work discloses the dual role of organotrifluoroborates serving both as a coupling partner and an electrolyte in C(sp3)–H functionalization.
Electrochemical oxidation-induced benzylic C(sp<sup>3</sup>)–H functionalization towards the atom-economic synthesis of oxazole heterocycles
作者:Na Yang、Anni Li、Hui Gao、Li-Mei Liao、Yu-Ping Yang、Pei-Long Wang、Hongji Li
DOI:10.1039/d2gc04782a
日期:——
(thio)xanthenes, nitriles, and water has been established in the absence of any catalyst or external oxidant. This electrochemical reaction features high atom economy and mild conditions, affording oxazole derivatives in moderate to good yields.